Maintaining the orbit will require continued fuel consumption.The page does not reveal if, after 12 months or 2 solar days they expect to simply run the tank dry and lose contact with the spacecraft, or what other sort of ending will follow. I have heard noproposals for extending the mission, but somewhere near the end - after completion of all the major objectivesa moment may come when otherwise unacceptable risks can be considered. My little suggestion represents just onepossibility - maybe not a very strong candidate, but if the mission can end with an attention-grabbing "goodbye" shot,there would be some value in that.

Dmuller, thanks for pointing out the big advantage in apparent size still enjoyed by the sun at the present time.

Thanks. I made them just before the first Messenger flyby. The correlation isn't perfect, but the filter combinations here are much more blue-shifted. The south pole view is just a rough overlay based on the color seen in the first two images.

Despite the title, it's mostly about what Messenger will do at Mercury, but it suggests that after Messenger and Bepi-Colombo, there won't be a lot gained by another orbiter. The next step would have to be a lander or sample-return mission.

Note that this suggests that Flyby #3 will cover more than half of the never-seen terrain.

I also note that the areas marked for Flyby #1 and Flyby #2 are backwards. Flyby #1 coverage is actually the area outlined in red on the image and Flyby #2 is outlined in blue, as we can see from the Flyby #2 coverage plan:

We knew that this flyby would be very similar to Flyby #1 -- so much that some of us had worried there would be nothing new to see at all. What's surprising (to me, anyway) is that the coverage on approach is much larger and significantly shifted compared to flyby #1 (and this is where almost all the new coverage comes from) but the coverage on departure is almost the same as for Flyby #1. Wonder why so much difference between the two?

This appears to be limited to press, but perhaps someone like Emily will be able to report back to us. :-)

Gosh, I'd missed the fact it was a telecon, not TV briefing. I'm glad you mentioned it -- got my request for the phone number in in time! I'll certainly be reporting on it. Today I'm working on my usual preview timeline.

I think maybe the reason the approach crescents are different is because on flyby 2 MESSENGER was coming in from a direction farther from the Sun -- its orbit has shrunk since then. But I don't have the best instinct for orbital geometry. If I don't think of a better question to ask, I may ask this one tomorrow.

I don't think so. According to my notes, it's flyby 2 and 3 that had the same geometry:

The two maps you point to are just centered on different longitudes.

Oops!

QUOTE (elakdawalla @ Sep 22 2009, 10:51 AM)

I think maybe the reason the approach crescents are different is because on flyby 2 MESSENGER was coming in from a direction farther from the Sun -- its orbit has shrunk since then. But I don't have the best instinct for orbital geometry. If I don't think of a better question to ask, I may ask this one tomorrow.

Actually, taking a look at the plots of the orbit, I think I can see it now:

The orbit "bends" a good bit more this time -- which makes sense, as Messenger is losing energy with each flyby. It's probably just a coincidence that the outbound path seems to be more or less the same (with respect to the planet surface) as it was for flyby #2. Especially since this flyby seems to be about 25 degrees further around Mercury's orbit than the last two were.

Because the spacecraft velocity relative to Mercury is about one-third slower at Mercury flyby 2 than at Mercury flyby 2, the gravity-assist turn angle to the spacecraft’s trajectory increases from about 27° to nearly 50°,” explains Jim McAdams, the MESSENGER mission design lead engineer. “This greater bend in the trajectory provided by the gravity of Mercury offers the spacecraft its first opportunity to view a small portion of Mercury’s surface twice with different vantage points and nearly identical lighting conditions just a few hours apart.

So I guess that's the answer. I'd still like to know exactly what percentage of Mercury will remain unimaged after this flyby . . .

1) This is their last chance to study the magneto tail in the equatorial plane.2) The flyby images are higher-resolution near the equator than any pictures Messenger will take later.3) They are still looking for possible moons, down to radius 100m.

Given the approach image we saw before, I think that means the lighted part of this crescent is mostly terrain that has never been imaged before, so that's kind of cool. Interesting-looking bright crater near the top.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted.
Do not reproduce without permission. Read
here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the
individual posters and do not necessarily reflect the opinions
of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer
UnmannedSpaceflight.com moderation team is wholly independent
of The Planetary Society. The Planetary Society has no influence
over decisions made by the UnmannedSpaceflight.com moderators.

SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society
and is funded by donations from visitors and members. Help keep
this forum up and running by contributing
here.